1. Field of the Invention
The present invention relates to a process to polymerize one or more monomers by means of one or more organic peroxides being dosed to the polymerization mixture at the reaction temperature.
2. Description of Related Art
Such a process is known from DE-OS-1 570 963. Herein it is taught to dose an initiator, optionally mixed with a solvent, to the composition being polymerized via a stream of water. The organic peroxides that are exemplified in this patent application are peroxydicarbonates and acetyl-cyclohexyl-sulfonyl-peroxide (ACSP). They are used at a temperature of 54xc2x0 C. The half-life of peroxy-dicarbonates at 54xc2x0 C. is known to vary from about 3.5 to 4.5 hours, depending on the type of peroxydicarbonate used.
This process of DE-OS-1 570 963 was found to solve a number of problems in the industry. However, the process still suffers from insufficient control of the heat peak of the polymerization reaction, a related less than optimal use of the reactor, a rather poor initiator efficiency, high residual peroxide levels in the resin produced, especially of the peroxydicarbonates, and/or the use of an undesirable initiator like ACSP which is known to lead, inter alia, to undesired fish eyes in the resin. A high residual peroxide concentration, especially of ACSP, is considered to correlate with a poor thermal stability of the resin containing it, which in turn is associated with a discolouration of the resin upon further processing. Accordingly, a different process not suffering from these drawbacks is desired.
Similarly, EP-A-0 096 365 discloses how a peroxide is added in three parts during the polymerization. Again, difficulties in controlling the heat that is subsequently generated are reported.
The current invention relates to a new process wherein these problems have largely been solved. More particularly, we have found that by selecting the proper organic peroxide and the proper dosing conditions, it is possible to obtain a polymerization reaction where the heat of polymerization is virtually constant over time, allowing optimum reactor space-time yield, very efficient peroxide usage, resulting in high polymer yields on the initiator, very low residual peroxide levels in the resin after polymerization, low fish-eye levels in the resin, and low reactor fouling. Accordingly, a resin with improved heat stability properties and low fish-eye levels was obtained, while the polymerization time could be shortened.